Stages of Fetal Development Week by Week

There is nothing more exciting when you are pregnant, than following the way your baby is growing inside you, from a tiny cell into a little person.

0-4 Weeks (one month)

The fertilised egg is very small, about 2mm, which is around the size of a dot. The cells are dividing and some blood vessels are forming. There isn’t a placenta yet, but the umbilical cord is beginning to form. The embryo is surrounded by amniotic fluid. Your breast may feel heavy and painful, like they do before you have a period. Now is the time to give up alcohol and smoking. Take Folic Acid, as this helps to prevent Spina Bifida, which effects the spinal cord. Vitamin D is also good for you to take at this time.


process pregnancy 1st 9th months fetal

5-8 Weeks (two months)

A lot has happened in a short amount of time. The little dot has increased in size and now measures around 9mm, the size of a pip in an apple. At this time your baby’s heart will start beating. There are lumps where baby’s eyes and ears will form. At about week seven, baby is the size of a grape and his hands and arms will soon appear. Now baby is a foetus and it is comfortable in its amniotic sac.

9 to 12 Weeks (three months)

By the ninth week your baby has increased in size, to about the size of a walnut. Now baby has tiny eyes and eyelids. By week ten he has lips and nostrils and it is continuing to grow and develop. Between weeks eleven and twelve, your baby begins to look more like a baby. He has hands, fingers and toes and his organs are developing and will all be present by week twelve. Your baby now has organs, limbs, muscles and bones.

13 to 16 Weeks (four months)

Baby is about the size of a plum and it now has little genitals. If you have a scan at this time it should be possible to tell whether it is a girl or a boy! Baby weights about 25 grams and is enjoying moving around. From about the fourteenth week he should measure around 85mm from his head to his bottom. The Midwife will be able to hear his heartbeat by using a heart rate monitor, you’ll hear it too!

17 to 20 weeks (five months)

Baby is getting much bigger now. It has eyelashes and eyebrows and he has started to produce urine by swallowing amniotic fluid, which then passes through his kidneys. He may respond to bright light or noises outside the womb. This is the time you may start to feel baby kicking and moving about. He also likes to suck his thumb and he may begin reaching up to grab the umbilical cord.

21 to 24 weeks (six months)

Baby weights about 350 grams now. He can hear your voice, so now is the time to start talking and singing to your growing bump. Baby is putting more weight on every day and he should be about 35cm long from the top of his head to his feet. He is also starting to develop more fat and muscle. He will also start to develop his taste buds and have preferences for the food you are eating.

25 to 28 Weeks (seven months)

This is the time when the baby’s digestive system and lungs begin to mature. Any baby that is born around this tie stands a good chance of survival. He should be around 35cm long, from the top of his head to his feet. You’ll notice your bump getting bigger as baby puts on more weight and develops more fat and muscle. At the end of 28 weeks he should weigh around one kilo.

29 to 32 Weeks (eight months)

Your baby can open his eyes now and he will turn to bright light outside the womb. His lungs are still developing and the hair and fat that covered his body before is starting to disappear. Baby will also have fingernails, which you may need to cut when he is born. He will still be moving about and kicking you.

33 to 36 weeks (nine months)

Baby’s nervous system is developed and his bones are becoming harder. Baby will be about the size of a melon now. He will be putting on weight rapidly. If he is a boy, then his testicles will start to come down into his scrotum.

37 to 40 weeks

Baby will now weigh about 2.7 kilos at thirty- seven weeks and by now, although there is less room he will still be moving about. His brain is fully developed and he will now start to move down into your pelvis, ready for birth. Most babies are born between 38 and 42 weeks and an average weight is between three and four kilos. Now it’s almost time to hold your baby for the first time!


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